An Etymological Dictionary of Astronomy and Astrophysics

The theory formulated by A. Einstein in 1905, which is based on the following two → postulates:

1. → Principle of relativity:
   The laws of physical phenomena are the same when studied in terms of two reference systems moving at a constant velocity relative to each other.
   

2. → Principle of constancy: The → velocity of light in free space is the same for all observers and is independent of the relative velocity of the source of light and the observer.
   

The term “special theory of relativity” refers to the restriction in the first postulate to reference systems moving at a constant velocity relative to each other (→ inertial reference frame). See also → general relativity.

See also: → special; → relativity.